This disclosure relates generally to a combined Brayton/Rankine cycle gas and steam turbine generating system operated in two closed loops from enhanced ground water or hot geothermal fluids and which burns only hydrogen and oxygen instead of a fossil fuel with air in the gas turbine.
Conventional combined cycle gas turbine power plants operate on natural gas or other hydrocarbon-based or fossil fuels combusted with air to heat a working fluid, usually feed water, to produce steam for operating turbine generators to produce electricity that is fed to a distribution grid to supply customers with electricity. Such plants produce waste heat that must be dissipated, typically in cooling towers, radiators, heat sinks, condensate reservoirs, etc. Even when waste heat can be transferred to the working fluid in some way or delivered to other uses such as heating systems, such mitigating techniques are only partly helpful in reducing inefficiencies. Other known inefficiencies in generating electricity using turbines include the limitations of using air as an oxidizing agent, the losses in portions of the system required to dissipate heat transfer working fluid and combustion air within the system, etc.
Electric generating plants operating on fossil fuels are also known to be substantial emitters of compounds that cause air pollution, chiefly carbon dioxide (CO2), silicon dioxide (SO2), nitric oxide (NO), and other substances such as dioxins, mercury, fly ash and other particulates, etc. Further, the use of hydrocarbon-based fuels such as petroleum, coal, and synthetics including “synthesis gas” or the so-called bio-diesel require large-scale mining, processing, and transport facilities and operations that are known to require very large capital investment, substantial uses of other non-renewable resources, or even cause significant environmental harm.
Most conventional power plants operate in open loop cycles. For example water, heated by boilers fired by hydrocarbon fuels, provides steam to drive turbines, which in turn drive generators to produce electricity. The waste heat contained in the spent steam exhausted from the turbine, while it may be utilized in heating plants or fed to cooling towers or reservoirs to dissipate the heat, is not recirculated back to the input of the system.
A classic closed loop system is the Brayton Cycle, first described by George Brayton for an oil burning engine in 1870. Note that a closed loop system is characterized by a system in which energy may be exchanged with its surroundings (across the system boundary) but the mass in the system remains constant, i.e., it is not exchanged with its surroundings or permitted to cross the system boundary. In a Brayton cycle, most often implemented in systems using a turbine fed by compressed air that is heated in a combustion section and allowed to expand in the turbine to spin its output shaft and a generator connected to it. Exhaust air from the turbine is then fed back to the input of the compressor through a heat exchanger. While the net change in mass in the system is zero (in an ideal closed system) because the working fluid—air—is returned to the input, the energy returned to the input will be diminished by the amount of heat converted to electricity in the system and the amount of heat given up to the surroundings because of system losses.
A number of schemes to recover the lost heat in such systems have been devised. In one method, a regenerator is used to transfer heat from the exhaust side to the compressed air routed to said combustion section. An intercooler may be used with two compressors operated in series by cooling the gas output from the first compressor before it enters the second one. The cooling increases the density of the compressed air thereby enhancing the compression ratio. In a third technique called reheating, used with two turbines operated in series by heating the exhaust from the first turbine before it enters the second one. The reheating increases the expansion ratio of the gases and thus the rotational drive to the generator.
Regardless of these enhancements, and the potential for more efficient generation of electricity in a closed loop system, inefficiencies remain, which limit the utility of closed loop systems. Heat losses are still significant, and the additional devices added to the basic system add complexity and cost. Yet, the use of gas turbine engines to generate electricity, while not new, because of their widespread use in aircraft and ocean-going vessels, and some power plant applications, may offer substantial economies because of their ready availability, reliability, etc. There appears to be significant promise for an electric generating system if a way could be found to operate a gas turbine engine in a closed loop using renewable energy by overcoming the inefficiencies in existing systems.
In one known closed loop system, recently developed by Sandia National Laboratories, a Brayton cycle gas turbine replaces air—the usual working fluid of a gas turbine engine—with supercritical carbon dioxide (CO2) as a working fluid, which is said to be capable of boosting conversion efficiency of said gas turbine assembly 118 portion of a compact generating system from approximately 40% to perhaps 50%. The increased efficiency results from the greater density of the supercritical CO2—similar to that of a liquid—as compared with air, which is a gas having a much lower density. The supercritical CO2, because of its greater density and much higher temperatures can convey greater amounts of heat to a gas turbine to generate more electricity. The efficiency increase enables correspondingly smaller footprints for the generating facility. However, accompanying the greater temperatures is a greater risk of corrosion in the gas turbine's components because of the presence of dilute carbonic acid.
To recap, existing power plant designs suffer from several disadvantages including (a) operation on fossil fuels—hydrocarbon-based substances that are not only non-renewable, but also, when burned, emit numerous by products into the atmosphere, contributing to climate change, environmental pollution, and potential harmful health effects. Further, (b) existing designs that burn fossil fuels to produce heat have relatively low efficiency, which results in depletion of non-renewable resources at a faster rate than is prudent. In addition, (c) measures employed to mitigate the inherent inefficiencies tend to be complex, reducing reliability and increasing costs of manufacture, installation, and maintenance. Moreover, (d) operating a Brayton cycle plant on supercritical CO2 risks shortened life and/or damage from the corrosion that results from the extremely high temperatures with this working fluid.
Other known designs include U.S. Pat. Nos. 5,687,559 and 5,775,091 and DE application number DE19808119A1. However, the current disclosure presents efficiency gains (such thermodynamic efficiency gains) as over these fillings.
What is needed is a generating system that operates with reduced environmental impact and contributions to air pollution, can rely on renewable resources and less on non-renewable resources, generates electricity with substantially greater efficiency and long life, has a compact footprint, and can be placed in operation and operated at lower costs.
This design can reduce the response time available to dispatchers to tenths of a second for a up to 10 mw increase compared to 4-5 minutes for 10 mw. Down ramp is even slower for the other designs unless the operator and dispatcher decide to vent steam. In this design, the electrolyzers ramp up to full load subtracting excess power while preserving it—operating losses for future use. The gas turbine shuts off fuel and assumes connections to perform as a motor load. Steam is recovered through the waste heat recovery system.
The prior art designs require dumping 100% of fuel while engaged in ramping down. The design also provides for independent adjustment of grid frequency and reactive power output when operating in AC mode. Projections from the current system show equipment response when the signal is received is less that the time required by dispatching to send the signal. The plant also provides system inertia replacing old coal and uneconomic nuclear plants.
None of the known inventions and patents, taken either singularly or in combination, is seen to describe the instant disclosure as claimed. Accordingly, it would be advantageous to have an improved cascaded gas and steam turbine generating system operated in a closed loop from enhanced ground water or geothermal fluids and which burns only hydrogen and oxygen instead of a fossil fuel with air in said gas turbine assembly 118.
Prior art mentioned in the international search report and disclosed in the included ISR include: US 201210185144 A1 (DRAPER) 19 Jul. 2012 (19.07.2012) entire document; US 201210023956 A1 (POPOVIC) 2 Feb. 2012 (02.02.2012) entire document; U.S. Pat. No. 6,910,335 B2 (VITERI et al) 28 Jun. 2005 (28.06.2005) entire document; U.S. Pat. No. 8,250,847 B2 (RAPP et al) 28 Aug. 2012 (28.08.2012) entire document; and US 2010/0326084 A1 (ANDERSON et al) 30 Dec. 2010 (30.12.2010) entire document.
Additionally, due to the prosecution history of the parent application to this patent, we include this analysis of prior art reference Viteri U.S. Pat. No. 6,910,335 B2.
Combined Brayton/Rankine Cycle Gas and Steam Turbine Generating System Operated in Two Closed Loops, from now on is referred as P1
Semi-Closed Brayton Cycle Gas Turbine Power System, from now on is referred as P2.
The key difference between the two patents are as follows:
P1 operates in a complete closed loop cycles, whereas P2 describes about a semi closed loop cycle
P1 consist of two cycles, a topping Braton cycle operating in closed loop and a bottoming Rankine Cycle operating in closed loop to enhance the efficiency of the system and reduce losses. P2 describes about a semi closed loop Bratton cycle with as the primary configuration and a possible additional configuration with a bottoming closed loop Rankine cycle.
P1 injects oxidizer and fuel in to the combustion chamber at desired operating pressure. P2 injects fuel in to the combustion chamber and oxidizer in to the compressor inlet.
P1 burns hydrogen and oxygen to generate steam. P2 burns hydrocarbon with oxidizer (air or oxygen) to generate steam, CO2, CO and other impurities depending on the fuel and oxidizer source.
Since P1 describes about a closed loop system and the working fluid is H2O in both cycles, no pollutants are released out of the system. P2 describes about a semi closed loop system with the working fluid as H2O, CO2 and other gases depending on the fuel and oxidizer used for the primary cycle and H2O for the bottoming cycle.
Since working fluid is a mixture of multiple gases in the primary cycle, they have to be separated (especially CO2 and other gases from the working fluid) and the polluting greenhouse gases like CO2 must be handled properly and stored.
P1 describes about a zero-pollution closed loop system, P2 describes about a semi closed system with reduced pollution when compared to a conventional system.
P1 generates hydrogen and oxygen by water electrolysis using renewable or excess electric power and stored in storage tanks. P2 derives oxygen from an air separation unit and used hydrocarbon fuels.
The Advantage and uniqueness of P1 over P2:
P1, operates in a closed loop cycle, which helps in eliminating the harmful polluting gases released into the environment. Making it more environmental friendly when compared to P2.
P1 propose to generate fuel and oxidizer using renewable power and excess electricity in the grid making it more reliable fuel source and enhances energy security, whereas P2 uses hydrocarbon fuels making it dependent on fossil fuels which are vulnerable to energy security.
P1 burns hydrogen and oxygen to generate steam which is allowed to pass through a gas turbine. P2 burns hydrocarbon and oxidizer to generate steam and other gases which is allowed to pass through gas turbine, potential problem being the possibility of forming corrosive gases when steam reacts with other gases in the combustion product which causes corrosion and erosion problems in the downstream equipment there by leading to premature failure of the system.
P2 requires an air separation unit, CO2 and other gas handling system that are extracted from the condenser, and they need to be compressed and stored in some safe facility to minimize the pollution from the system operation, thereby increasing the initial investment cost and operation cost and drop in efficiency as these processes requires energy.
Likewise, we address U.S. Pat. No. 5,331,806.
Combined Brayton/Rankine Cycle Gas and Steam Turbine Generating System Operated in Two Closed Loops, from now on is referred as P1
Hydrogen Fuelled Gas Turbine, from now on is referred as P3.
The key difference between the two patents are as follows:
P1 is a closed loop, combined cycle configuration, where as P3 is a closed loop Brayton cycle configuration.
P1 burns H2 and O2 and cools the flame with water and steam injection to desired temperature and allow it to pass through the gas turbine, since the gas turbine exit steam is hot, it is furthered allowed to pass through a heat exchanger where heat from the turbine exit's low pressure high temperature steam is used to convert high pressure water in to high pressure high temperature steam and used in bottoming Rankine cycle. There by enhancing the heat recovery rate and improving the overall efficiency of the cycle over the configuration as described in P3.
P3 burns hydrogen and O2 and dilutes the flame with steam to achieve desired temperature at combustion chamber outlet and then allow it to pass through the gas turbine, the hot gas turbine exit steam is redirected to the compressor inlet where it is compressed and reinjected into the combustion chamber. The key problem is high steam compression requires a lot of energy and compressor needs to be designed to handle high temperature steam as a typical compressor blades are designed to operate at approximately 450 C, whereas according to P3's description, the steam entering the gas compressor will likely to exceed that temperature.
P3 describes that water is injected in to the compressor to reduce the steam temperature during compression process, but in order to cool the steam substantial amount of water needs to be injected which leads to improper mass balance, oversized compressor and corrosion problems. P1 handles this issue by reducing the temperature of inlet steam in to the compressor and reducing the mass flow of steam into the compressor by optimizing the cooling steam and cooling water flow in the system.
If P3 tries to reduce their compressor steam inlet temperature, then a significant amount of water is needed to bring down the temperature in a condenser, which would increase the auxiliary water requirement (condenser cooling water) for the system.